The research program outlined in this proposal embodies our commitment to the synthesis of architecturally challenging, pharmacologically significant natural and non-natural products. Our entry into this arena comes not only from a desire to synthesize bioactive agents but also from a fascination with the development of concise organic synthesis strategies and efficient synthetic methodology. These areas of study will not only impact organic chemistry but also the development of new medicines and the understanding of biological processes. Specific to this program are strategies to medicinally interesting polycyclic ether natural andnon- natural products that involve C-glycoside/ketoside synthesis and enol ether-olefin ring-closing metathesis. The first part of this proposal outlines our synthesis of members of the marine ladder toxin family, specifically, gambieric acid and brevenal. These agents are non-toxic polycyclic ethers isolated from dinoflagellates that, in preliminary studies, have demonstrated the somewhat puzzling ability to displace one of the brevetoxins from its target (voltage gated sodium channels) in the absence of neurotoxicity. Interestingly, both of these agents have demonstrated other biological activity that could prove to be important to human health (anti-fungal activity for gambieric acid and the ability to clear mucous from sheep lungs as a model for cystic fibrosis for brevenal). Also outlined is a program targeting the generation of polycyclic ether libraries in an effort to gain a better understanding of their unique biology. This application also contains our proposal to expand the C-glycoside, metathesis chemistry to medicinally relevant non-ladder toxin natural products. Specifically, we are interested in the actin binding pectenotoxin family. That actin binders have been shown to target cells lacking the p53 protein makes the pectenotoxins excellent anticancer leads and our efforts in this area potentially important.